In portable devices such as pagers, a radio frequency signal having information modulated at a predetermined baud rate is used to communicate paging information. Since pagers are miniature and portable, it is desirable to use miniature batteries for a power source. It follows that it is desirable to conserve battery power in order that the battery life of the pager be maximized. Since a paging signal is sometimes present and sometimes absent, it is desirable to provide a pager capable of reliably determining the presence or absence of the paging signal while consuming as little battery power as possible.
When using a baud rate detector, the absence of a signal may in most cases be determined rapidly. As soon as the absence is detected, the receiver portion of the pager is switched off, thereby conserving battery power. However, due to statistical characteristics of the noise or undesirable signals at other baud rates, they may falsely appear as the predetermined baud rate of the desired signal. A determination of the absence of the desired signal as being the desired signal is referred to as falsing. False detection of a signal consumes excessive power because the pager then continues to operate the receiver for an extended period of time attempting to synchronize to the signal when in fact, the desired signal is not present.
Thus, what is needed is a method and apparatus capable of rapidly detecting the absence of the signal while reducing falsing.